HIGH MAST LIGHTING

High mast lighting is described as being the accepted term for a form of lighting which infers a mounting height of 20 M and above, with heights of 25 M and 30 M predominating, the use of tubular or tapered steel masts, usually equipped with a winch system to raise and lower the lighting equipment, and clusters of lanterns which are specifically designed for this installation. The author outlines the history and present trends of such lighting since its inception in the UK 14 years ago, and in so doing provides information on installations both in the UK and overseas, not only in highway situations but also at other locations. The early installations included the use of 1 kw colour-corrected mercury lamps, with groups of 4 or 5 lamps at a beam angle of 45 deg to provide a glare-free uniform illuminance with a minimum level of about 20 lux over the whole area to be lit. The development of new light sources is described, which includes the introduction of 400 w and 600 w high pressure sodium lamps to provide approximately the same lumen output as the original lamps. The beam angle has also been increased to 54 deg. The development of new designs in winch systems is discussed, which has led to the introduction of units which are self-sustaining with automatic brakes to provide greater safety, and which incorporates a sealed gear box lubricated for life. The flexible multi-core electrical cable runs over a pulley in the mast head, with a plug and socket housed in the base compartment. This cable moves up and down with the stainless steel hoisting ropes. /TRRL/